Main Body of Report

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CHAPTER 1

INTRODUCTION

1.1 Introduction

The geotechnical engineers for tall earth dams sometimes come across with

problem such as excessive settlement after construction. Although it is a timelyprocess with slow straining, but it still brings problem, for instance crack on

earth dams which can cause damage and in more extreme cases, it can trigger

disaster. The root of this problem is the soil particles break because down

below the structure, the confining pressure is very high and it can be up to 70

MPa (Yamamuro and Lade, 1996). This phenomenon is closely related to

creep behavior and particle breakage is the cause of creep.

This research focused on particle breakage on granular soils. Granular soils can

be found in natural slope, foundation base and embankments. It is subjected to

static and dynamics loads and the loads can cause particle breakage. Particle

breakage is a phenomenon where the soil particles transform to finer state due

to slippage, dilation and creep. It is an important parameter in soil mechanics

as it can affect the permeability behavior especially under the earth dams.

Moreover, particle breakage can affect the stress-strain curve and this is the

main focus in this study. The behavior of stress-strain curve is no more typical

if particle breakage commence. It is still not well understood. The most

important effect of particle breakage is it maybe reduces the soil strength.

Hence it is vital to understand this behavior; therefore it can enhance the

knowledge on the effect of particle breakage to the stress-strain curve.

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The particle breakage problem is modeled on laboratory via triaxial test. The

test is conducted on compacted sands in order to replicate the possible soil

condition below the earth dams. The consolidated isotropically drained (CID)

triaxial test is used in this study. The specimens are made up of quartz sand

with diameter 600m, 1.18mm and 2 mm. The applied effective stresses are

50kPa, 100kPa, 200kPa, 300kPa and 400kPa. Sieve analysis is conducted

before and after the test in order to observe the particle breakage. During

shearing stage, microphone is installed at the cell body to record the breakage

sound. The data is analyzed based on the particle size distribution, breakage

indicator (sound recorded), stress-strain curve, volume change during shearing

stage and the shape of shear strength failure envelope in Mohr circle due to

effect of breakage.

1.2 Problem Statement

There is not much research has been conducted in order to understand the

effect of breakage to the stress-strain curve. The effect of particle breakage

during shearing in triaxial test has a direct effect on the resultant stress-strain

curve. This effect is still less understood since the deviator stress still

continuously increase with shear strain when high confining pressure is

applied. Moreover, it influences the Mohr circle in the way that the resultant

shear strength failure envelope curve is less steep compared with Mohr circle

without effect of particle breakage. The decrease in friction angle will cause

decrease in strength too. Hence, it is essential to conduct a study on the effect

of particle breakage on the stress-strain behavior which will in turn affect theshear strength behaviour. This research is intended to study on how particle

breakage affects the shear strength of soil. Hence, this research will enhance

the understanding on the effect of breakage on the stress-strain curve that may

be related to the settlement and creep behavior.

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1.3 Objectives

The aim of this research is to study on how particle breakage affects the shear

strength behaviour. The specific objectives of the research are

1. To conduct CID triaxial tests on course grained soils at low (< 300 kPa)

and high (> 300 kPa) confining pressures.

2. To determine the shape of the shear strength envelope in effect of

particle breakage.

3. To justify particle breakage through particle size distribution curve

before and after triaxial test.

4. To detect particle breakage using Sony Sound Forge software.

1.4 Scope of Work

This research is based on laboratory test. The test is conducted at Advance Soil

Mechanics Laboratory, UiTM Shah Alam. The scope of work is given in

Figure 1.1. The research starts with problem formulation in order to find out

the problem statement and objectives of the research. The literature review,

methodology, data gathering, data analysis, discussion and conclusion are the

body of the report.

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Figure 1.1: The Scope of Work

4

LITERATURE REVIEW

RESEARCH DESIGN AND METHODOLOGY

Triaxial test

Breakage sound recording

DATA GATHERING

DATA ANALYSIS

PROBLEM FORMULATION

Problem statement


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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

The study on particle breakage of soil is so significant in understanding

geotechnical problems, such as dilatancy and creep of soil. The particlebreakage or known as grain crushing is always related to the granular type of

soil. The particle arrangement in granular material is vulnerable to particle

breakage if high confining pressure is imposed on the soil. Research also found

out that the particle breakage is common in all sands (Coop, 1999). It is

because particle breakage can happen due to the angularity, coarseness and

uniformity of gradation (Bohac et.al, 2001). The granular material has these

properties; hence it is exposed to the particle breakage phenomenon compared

to clay soil. In describing the phenomenon of particle breakage, there are two

important terms governing the principle of particle breakage. There are

dilatancy and creep.

2.2 Dilatancy

Dilatancy is defined as the expansion of specimen due to the particles that

move over to each other during shearing. Dilatancy is an important term in

understanding particle breakage. The term dilatancy was coined out by

Reynolds in year 1885. He said that in the process of plastic deformation, the

dense granular material will increase their volume and dilate. But for loose

material, there will be decreased the volume in the plastic deformation process.

This can be described as the specimen will enlarge due to the void that

appeared between the soil particles. The effect will be obvious in the stress

strain curve. When the sand specimen is loaded in the triaxial test, the

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specimen will increase the volume because of increasing volume of void

between the sand particles. It is explained by Oda et.al (1998) and Descrues

et.al(1996) that there is particle rotation and it increases the volume of void. It

resulted from the process of particle rearrangement including rolling and

translation (Wan and Guo, 2004). The process of dilatancy is illustrated in

Figure 2.1. When the sand specimen is undergoing shearing process in triaxial

test, the soil particles will rearrange themselves to denser state. The void in the

specimen is reduced. At this point, the particles only fill the void, but when

dilation happened in dense sand, the soil particles will roll over to each other. It

cause greater strength must be reached before the sand particles rearranged

back to stable state. This is where the peak strength is achieved in the stress-

strain curve that cause by shearing. The degree of dilation is higher just before

the peak strength. The strength is reduced after the peak strength because the

sand particles are compressed until shear stress become constant. Figure 2.2

shows the stress-strain curve for loose and dense sand. The different between

dense and loose sand specimen are the arrangement of the sand particles, hence

they will exhibit different behavior. For dense sand, there is an obvious peak

strength point, whereas for loose sand, the peak strength is not clear. This is

because when the specimen is loaded, the loose sand will shrink. It does not

experience dilation process. Therefore, the peak strength achieved by these two

soil condition is different. Dense sand will produce higher peak strength due to

resistance provided by dilation. The behavior of dense and loose sand also will

be different as different stress level is imposed to the soil. High stress level will

diminish the dilatancy effect. Particle breakage will take place in this plastic

deformation process. Particle breakage is a unique mechanism of deformationinstead of simple slip. It cause reduction in angle of friction and also affects the

shear strength of soil (Simonini, 1996).

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Figure 2.1: The Process of Dilation

7

Loose sand Dense sand

Dense sand DILATION

Axial load

Axial load


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Figure 2.2: The Stress-strain Curve for Loose and Dense Sand

In the stress-strain, the dilatancy is denoted by the peak point of the curve.

However, for the test that involved high confining pressure, there is continuous

increase of shear strain. There are some researches encounter this problem, but

particle breakage is not proved yet to be the cause of the continuous increase of

shear strain. Hence, this study will prove the particle breakage by recording thesound produce when soil particles break.

8

Axial strain, a

Dense sand

Loose sand

High rate

of dilation

region

Deviator

stress, d


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2.3 Creep

Creep is again a reduction in volume under constant stress. When soils

experiencing constant state of load or stress, the soil continuously deform and

move. It is known as viscous creep behavior. Creep can cause failure if three

stages of deformations took place. They are sequential primary, secondary and

tertiary periods. However, soil is rarely experiencing secondary period. The

strain rate of soil is either decrease continuously after first loading is applied or

increase at the onset of failure. It is term as creep rupture (Kuhn and Mitchell,

1993).

Creep gives a long term effect to the soil and structures. It cause long term

deformation and pressure on the building structures, bridge abutments, earth

retaining structures and earth slope. If excessive deformation with time occurs,

then it can cause failure (Lade and Liu, 1998). From previous researches

conducted, it can be seen that all soils creep, but the amount of creep is

different depending on the type of soil (Lade and Liu, 1998). According to

Muruyama et.al(1984) and Lade et.al(1997), sands creep less than clays at the

same stress states. The amount of creep increases with confining pressure, most

importantly when particle breakage happened at high stresses (Yamamuro and

Lade, 1993).

Nowadays, creep can be accounted by laboratory test, field test or using Finite

Element Method. However, it is more reliable to conduct field test because thetest is more representative of the actual creep behavior. But there is no specific

apparatus to measure the rate of creep in field. There were some attempts, for

instance, Baguelin et.al(1978), Ladanyi and Johnston (1973), Kjartanson et. al

(1990) and Bahar and Cambou (1995) have quantified creep in field by using

pressuremeter. Bahar and Cambou (1995) have conducted pressuremeter test

and the data is compared with computer program generated by Finite Element

Method. Figure 2.3 shows the comparison between predicted creep settlement

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and in-situ measurement for building (Bahar and Cambou, 1995). From the

result obtained, there was only a slight agreement between field data and

prediction from Finite Element Method. However, at least it is still a useful

tool to predict creep behavior.

Figure 2.3: The Comparison between Predicted Creep Settlement and In-situ

Measurement for Building (Bahar and Cambou, 1995)

2.4 The Particle Size Distribution

The particle size distribution is carried out before and after triaxial test. The increase

in the percentage of finer particle after the test will indicate that the particle breakage

occur during the test. This is a suitable measurement to justify the particle breakage

(Hardin, 1985). Figure 2.4 shows the example of particle size distribution graph for

specimen that experience particle breakage (Feda, 1971).

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Figure 2.4: The Example of Particle Size Distribution Graph For Specimen That

Experience Particle Breakage (Feda, 1971)

From Figure 2.4, it can be seen that the curve 1 represented the particle size

distribution before particle breakage occur while curve 2 is the particle size

distribution after particle breakage occur. The different of these curves is that

the particle size distribution on curve 2 is less steep compared to curve 1. It

indicates that the finer particles are produced in the particle breakage process.

2.5 Factor Affecting Particle Breakage

Particle breakage is affected by several factors. There are the effect of the

stress, size, angularity, grade and hardness of granular material (Lade et.al,1996). Factor affecting particle breakage is tabulated in Table 2.1.

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Table 2.1: Factor Affecting Particle Breakage

1Stress Stress level Higher stress level produce more breakage

Stress magnitudeBreakage decreases with time under constant

stress magnitude (known as creep)

2 Size

Larger size Larger particle produce more breakage

Smaller size Smaller particle produce less breakage

3

Angularity More angularity More angularity sand produce more breakage

Less angularity Less angularity sand produce less breakage

4Grade

Well graded Well graded not break easily

Uniform Uniform graded breaks easily

5

Hardness

Hardness increase, rate of breakage will decrease

The particle breakage is affected by the stress level and magnitude. The higher

stress level will cause more breakage as more energy is transmitted through the

sand particles. Particle breakage is a function of time. The breakage is

continuing under constant stress but in decreasing rate. It is also known as

creep. The varying particle size produce different amount of breakage. Larger

particle will break easily compared to smaller particle. This is due to the

existence of flaws or defects that might be the cause of breakage in large sand

particle. The smaller particles are the result of the breakage, hence it has fewer

defects. So the smaller particle become tougher as breakage continues for

subdivided particles.

In term of angularity, the angular particle will break easily compared to the less

angular particle. It is because the concentrated stress will occur along their

narrow dimension and at the angular contact. It cause fractured to the particle.

Another factor is the grade of the soil. The uniform soils will break easily than

well graded soils. It is because the relative density of uniform soils is lower

than well graded soils. In well graded soils, there is more contact between

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particles, hence the average contact stress will lesser. The uniform soils are

more vulnerable to breakage because it has less contact; hence the average

contact stress is higher. In term of hardness, the harder the sand particle, the

lesser breakage will be experienced by the sand particle. The hardness will

exhibit how strong the particle will be due to stress (Lade et.al, 1996).

The particle breakage is also affected by the condition of soil whether it is in

loose or dense state. The loose sand exhibits higher breakage than dense sand.

It is due to the slippage of the sand. The particle of loose sands is unstable and

slippage can occur easily, hence produce more breakage (Lade and Liu, 1998).

Another factor is the test condition. The undrained and drained condition also

affected breakage. Drained test is observed to produce more particle breakage.

This is because the undrained shearing stage will maintain the void ratio and

the volume. Therefore, there is not much room for the particle to dilate and

break. On high pressure test, the undrained test produces less breakage too

compared to drained test. This is due to the fact that the average mean normal

effective stress is lower in the undrained test. It is because of the development

of large positive pore pressure, therefore the normal effective stress will be

lower (Lade et.al, 1996).

A study conducted by Ramil and Miura (2004) shows that there is effect on

particle breakage due to the degree of saturation. The study is done on volcanic

soils that composed of sand. The particle breakage is more dominant in wetsand. However, the result seems to be different to other types of sand,

especially quartz sand. It is because the physical properties of volcanic soils are

different as water can enervates volcanic soils and this cause the sand particles

to break easily.

2.6 The Effect of Particle Breakage

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The effect of the particle breakage according to Billam (1971) includes the

principle effective stress ratio at failure decreases with the increasing confining

pressure. Moreover, there is a large volume reduction especially during shear.

It causes the increase in axial strain to reach failure. Also, the particle breakage

will result finer particle, hence reduce permeability. The grain distribution after

particle breakage will show a mix of fine and medium sized soil particles. An

important point highlighted by Billam (1971) is the larger grains experience

less breakage compared to the finer soil particles, even at high pressure.

According to the study done by Indraratna and Salim (2002), the particle

breakage also happened in low confining stresses especially to the courser

grain. It is because fewer contact between soil particle cause high interparticle

stresses and asperity breakage.

Particle breakage was understood to stop after stable grading is achieved

(Baharom and Stallebrass, 1998). However, a study done by Luzzani and Coop

(2002) revealed that particle breakage will only stop as a result of

counteracting components of volumetric strain and not because stable grading

is achieved. This conclusion is made as the test conducted by Luzzani and

Coop (2002) used ring shear tests that able to reach higher stress level than one

did by Baharom and Stallebrass (1998) who used triaxial test. But it is still not

justify whether particle breakage will stop after stable grading is achieved as

the ring shear tests unable to reach to that extent. However, Hardin (1985)

suggested that particle breakage will only stop when stable grading and

volumetric strain ceased. The improvement work was made then by Coop et. al(2004) to reach higher level stress in order to achieve stable grading. The

conclusion pointed out by Coop et. al (2004) is at high pressure, particle

breakage continues to very large strain. The particle breakage is accompanied

by volumetric compression. A constant grading is achieved at very large strain

but it is dependent on normal stress applied and uniformity and absolute

particle size of the initial grading.

2.7 The Past Researches on Particle Breakage

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The study on particle breakage was started since 1920. Blackwelder (1920)

conducted compression test on deeply buried oil-field sand. He concluded that

particle breakage is not significant even at stresses much higher than 7MPa.

Terzaghi (1925) said particle breakage not occurs in natural sand and no

engineering problems encountered such high stresses. However, in the extreme

technology engineering nowadays, everything is possible. The engineering

applications demanded research on particle breakage as it is important to solve

problems such as settlement of tall earth dams, which involved pressure as high

as 70MPa (Yamamuro and Lade, 1996).

Particle breakage indices have been introduced by Marshal (1967), Lee and

Farhoomand (1967) and Hardin (1985) to quantify amount of breakage. These

indices are emphirical and depend on the changes of particle sizes. The

important of the researches are to solve permeability of sand under tall earth

dam. Moreover, the small particles resulted from the breakage will clog in the

filter material, hence it demanded for researches on quantification of the

particle breakage. Research on particle breakage have been conducted by

Harireche and McDowell (2003) to prove that plastic hardening under

monotonic loading is due to particle breakage. The research examines the

discrete element modeling of cyclic loading on aggregate.

The researches on particle breakage are closely related to creep of soil. In fact,

creep is cause by particle breakage. The researches mainly intended toformulate the equation for creep. Findings showed that creep strain is

proportional to the logarithm of time [McDowell and Khan (2003); Lade and

Liu (1998); Atkinson (1993); Powrie (1997)]. It is given by:

= C log t/to . (2.1)

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where to is the time of measurement begin. Kuhn and Mitchell (1993) proved

that creep behavior is also cause by viscous and frictional particle sliding. The

work is conducted via rate process theory. These researches on creep

implemented one dimensional normal compression test.

The investigation on pile tips also takes into account the effect of particle

breakage to the pile settlement. The test were carried out by BCP Committee

(1971) and Mazzucato and Ricceri (1986). The study by Simonini (1996) has

incorporated Finite Element Method to analyze the problem related to particle

breakage on the pile tips. The research can help in prediction of strength,

dilatancy and particle breakage in the soil surrounding the pile base.

2.8 The Effect of Particle Breakage on the Stress-Strain Curve

The effect of particle breakage to the stress-strain curve is significant as it will

affect the strength of soil. The stress-strain curve is observed to be in different

state for the test conducted for low and high stresses. The test on low stresses

exhibit peak strength for dense sand and a constant state without peak strength

for loose sand. The test involve high stresses demonstrate the behavior as loose

sand even the sample is prepared in dense state. It is because the effect of

dilation is diminished as high stress is imposed on sample.

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Figure 2.5: The Effect of Particle Breakage on the Stress Strain Curve

(Bohac, 2001)

Figure 2.5 shows the effect of particle breakage on the stress strain curve. The

graph represented dimensionless shear stress versus displacement. The result is

taken from oedometer test conducted on granular soil. From the graph, it can

be seen that the soil experiencing failures at the same shear stress. However,

the displacements are varied because of the different values of normal stress.

There is the increase of displacement value with the increase of normal stress.

It is expected that the specimen is having particle breakage stage after high

confining pressure is applied. The effect of breakage will give effect to the

value of displacement as the soil particles structure changed after the soil

particles break into smaller grain. The constant-volume state can be seen in the

test. It is a result of counteracting dilative strains from particle rearrangement

and compressive strains from particle breakage (Coop et.al, 2004).

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According to Simonini (1996), there are significant changes in the stress-strain

curve in triaxial compression due to particle breakage. The sharpness of the

peak-softening behavior diminished and the stress-strain behavior become

strain-hardening type only. That is why the stress will continuously increase at

high stress level. As dilation is vanished because of high stress level, dense

sand also will exhibit the same shape of stress-strain curve as loose sand. The

study conducted by Yamamuro and Lade (1996) has revealed that in high

stress, the stress strain curve will continuously increase without dilation effect.

Moreover, increasing confining pressure will cause initial slopes of the stress-

strain curve to flatten, the maximum principle effective stress ratios decrease,

the amount of volumetric compression increase and axial strain at failure

increase. The flatten section is contributed by particle reorientation and

breakage during loading (Billam, 1971). Figure 2.6 shows the stress-strain

curve at high pressure (Yamamuro and Lade, 1996).

Figure 2.6: The Stress-Strain Curve at High Pressure

(Yamamuro and Lade, 1996)

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Major principle strain (%)


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However, there is not much work have been conducted regarding to the effect

of particle breakage to the stress strain curve. It is important to understand the

effect of particle breakage to the stress strain curve because particle breakage

affected true strength value of the sand (Whitlow, 2001; Ramil and Miura,

2004).

Figure 2.7 shows the consolidation isotropically drained test under applied

pressures. The major stresses acting on specimens are deviator stress (denoted

by force/ ram area), cell pressure and pore water pressure. From the test, the

result is analyzed to produce stress-strain curve and Mohr circle graph. The

calculation of major principle effective stress, 1 is given in Equation 2.2.

wdu+=

31' (2.2)

where:-

1 = major principle effective stress

d = deviator stress

3 = minor principle effective stress

uw = pore water pressure

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Figure 2.7: The Consolidation Isotropically Drained Test under Applied

Pressures

20

Cell

pressure,3

Deviator stress,

d

Pore water

pressure, uw


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CHAPTER 3

RESEARCH METHODOLOGY

This research is based on laboratory test. The tests conducted in this research are

consolidation isotropically drained (CID) triaxial test on quartz sand with different

grain size. The diameter of the specimen is 0.6mm, 1.18mm and 2mm. There are 15specimen tested. Confining pressure 50kPa, 100kPa, 200kPa, 300kPa and 400kPa are

applied on each grain size. The specimen is undergoing dry sieve analysis before and

after the test in order to quantify particle breakage. The particle breakage is also

detected via sound recording during shearing stage. Then the results are analyzed and

the stress-strain curve is plotted. Besides that, the Mohr circle is plotted in order to

identify the strength characteristics. Figure 3.1 shows the methodology of the

research.

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Figure 3.1: The Methodology of the Research

22

METHODOLOGY

Dry sieve analysis CID testBreakage sound

recording

It is conducted

before and after

test15 specimens, 5

specimens for

0.6mm, 1.18mm

and 2mm each.

The confiningpressure applied

are 50kPa, 100kPa,

200kPa, 300kPa

and 400kPa

The sound

recording is

conducted via

Sony Sound Forge

software during

shearing stage

DATA ANALYSIS

Particle size

distribution

Stress-strain curve

Mohr circles are

plotted for each

specimen

Breakage indicator

during shearing

stage

DISCUSSION AND CONCLUSION


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3.1 Specimens

The specimens used in the research are made of quartz sand. Quartz sand is

identified through physical characterization. It has glassy, lusty and grey in

colour. The sand is undergoing sieving process in order to obtain the uniform

size of 600m, 1.18mm and 2.0mm.Appendix A shows the particle size

distribution of raw samples. The quartz sand is selected because it has better

strength, hence the particle breakage can be easily identified through sieve

analysis. Moreover, the strength of this sand will produce higher frequency of

breakage sound. Hence, it made easier for breakage sound detection. Plate 3.1

shows the specimen for the test.

Plate 3.1: The Specimens for

the Test

3.2 The Consolidated

Isotropically Drained Triaxial

Test

The consolidation isotropically drained test (CID test) is conducted to the

specimens. Plate 3.2 shows the test set up and Figure 3.2 shows the schematic

diagram of consolidation isotropically drained triaxial test (CID test). These

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specimens are imposed with effective stresses 50kPa, 100kPa, 200kPa, 300kPa

and 400kPa. The triaxial test is conducted in accordance with BS 1377 (1990).

Plate 3.2: The Test Set Up

24

Specimen volume

change unit

Deviator stress

= q

Soil specimen


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Figure 3.2: The Schematic Diagram of Consolidation Isotropically Drained

Triaxial Test (CID Test)

The consolidation isotropically drained triaxial test (CID test) consists of four

main stages. The first stage is the preparation stage. In this stage, the specimen

is installed on the base. The rubber membrane is stretched to form cylinder

shape by the help of split former. It is important to ensure that there is no

trapped air between the rubber membrane and the split former wall. Then, the

sand is poured in the stretched rubber membrane. The sand is poured in fivelayers. Each layer is compacted by using wood compacter and a steel rod. For

the first time of the test, the specimen is taken out for sieving test. It is to

ensure that there is no particle breakage caused by the compacting effort. It is

observed that 10 numbers of blows for each layer not caused breakage to the

sand specimen. The compaction work is conducted in order to exhibit dense

sand specimen. After the specimen is set up, cell body is installed and water is

25

Acoustic

sensor

installed on the

cell wall

Pore water pressure

measurement

Filling with de-aired

and de-ionised water

Load cell

attached

to ram


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drained into the cell body. Then, the second stage which is saturation takes

place.

The saturation stage is conducted by applying pressures to the specimen. B-

value is checked and a minimum value of 0.97 indicates full saturation. Cell

pressure and back pressure is applied until the required effective stress is

achieved. Then the specimen has undergone consolidation stage. After

sufficient consolidation is achieved, the shear stage commenced at speed 0.03

mm/min. At this stage, the acoustic sensor is installed on the cell wall to record

the sound produced due to particle breakage. After the sheared specimen oven

dried, the dry sieving is conducted to the specimen. It is to indicate that there is

particle breakage occur during shearing stage, besides recording the sound

produce during shearing.

Consolidation isotropically drained triaxial test is selected because many

engineering problems deal with drained condition, such as building, bridge

abutments, earth retaining structure and earth slope (Lade and Liu, 1998).

However, undrained condition can exist in case that permeability of

cohesiveless soil is relatively low in fine sands or silts (Lade and Yamamuro,

1996).

The specimen is prepared to exhibit dense sand. In doing so, the specimen iscarefully compacted in five layers. Precaution is taken while compact the

specimen as particle breakage is prohibited at this stage. To replicate the dense

sand condition, the specimen is compacted using a wood compacter and a steel

rod. Plate 3.3 shows the compaction equipments. Then the specimen is taken

out for dry sieving in order to verify whether there is breakage occur cause by

compacting effort. The test proceeds after no breakage is detected and the 10

number of blows per layer in uniformly applied for other specimens.

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Plate 3.3: The Compaction Equipments

3.3 Particle Breakage Sound Detection System

In order to measure the sound produce when breakage commence, acousticsensor is placed at the cell body of the triaxial equipment. The acoustic sensor

is connected to the computer and the sound recorded by using Sony Sound

Forge software.

3.4 Dry Sieve Analysis

The specimens undergo dry sieve analysis process before and after the triaxial

test. It is to identify the difference of the particle size distribution before and

after the test. Sieve analysis will be conducted and it is in accordance with BS

1377 (1990). The data is gathered and analyzed. The results justify on the

particle breakage of the specimen after the test.

CHAPTER 4

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RESULTS AND ANALYSIS

4.1 Particle Size Distribution

For all specimen tested, all of them experience particle breakage. Before test,

all of the specimens consist of uniform graded sand. Figure 4.1 shows the

particle size distribution for size 600 m with effective stress 50kPa. Appendix

B-1 shows the particle size distribution for size 600 m with effective stress

100kPa, 200kPa, 300kPa and 400kPa respectively, Appendix B-2 show the

particle size distribution for size 1.18mm with effective stress 50kPa, 100kPa,

200kPa, 300kPa and 400kPa respectively and Appendix B-3 show the particle

size distribution for size 2mm with effective stress 50kPa, 100kPa, 200kPa,

300kPa and 400kPa respectively. The raw data for particle size distribution

after test is given in Appendix C.

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4.2 Stress-Strain Curve, Volume Change Behavior and Particle Breakage

Indication via Sound Recording

The breakage indicator, stress-strain curve and volume change behaviour

during shearing for size 0.6mm are given in Figure 4.2 (a), (b), (c), (d) and (e)

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with effective stress 50kPa, 100kPa, 200kPa, 300kPa and 400kPa respectively.

Figure 4.3 (a), (b), (c), (d) and (e) show the breakage indicator, stress-strain

curve and volume change behaviour during shearing for size 1.18mm with

effective stress 50kPa, 100kPa, 200kPa, 300kPa and 400kPa respectively.

Figure 4.4 (a), (b), (c), (d) and (e) show the breakage indicator, stress-strain

curve and volume change behaviour during shearing for size 2mm with

effective stress 50kPa, 100kPa, 200kPa, 300kPa and 400kPa respectively.

Appendix D shows the deviator stress with membrane penetration correction

while Appendix E shows the specimens after test.

From the results obtained, it can be seen that there is particle breakage occur

before peak strength. This is due to the dilation process in which the angular

sand particles roll to each other to accommodate the load applied. The particles

break into smaller grain during dilation process. The particle breakage

continues after the peak strength until constant stress is achieved. The stress-

strain curve strained under constant stress and particle breakage will continue

and this is a form of creep deformation. This is where the settlement occurs in

slow strain. It is a problem faced in tall earth dam construction in a long run.

Besides settlement problem, it also gives effect on the permeability under the

earth dam. When finer particle produced due to breakage, the permeability

under the dam will be less.

The breakage indicator makes possible to identify the particle breakagebehaviour during shearing stage. The breakage sound recording work is not an

easy task because it required expect who really understand about sound

recording. It involved a lot of preliminary works in order to get the best setting

before the breakage indicator can be presented effectively on paper. In doing

so, there are some specimens which cannot get the best sound recording results.

For instance, specimen with effective stress 50kPa for size 0.6mm has very

little signal to be analyzed because the setting on the software is not really

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good. However, it still can give breakage indications in certain part of the

stress-strain curve. There is a different problem faced for specimen that

recorded high frequency throughout the test. The breakage indications are not

really clear because of the noise resulted from the triaxial machine. However,

after analysis is made on the sound, it is clear that the breakage sound produced

higher frequency than the triaxial machine sound. So, the particle breakage still

can be observed.

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Breakageindicator


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Dev.stress(kPa) vs Axial strain(%)

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)

Vol.change(ml) vs Axial strain (%)

-2

0

2

4

6

8

10

12

14

0 5 10 15 20

Axial strain (%)

Volumechange(ml)

Figure 4.2 (a): The Breakage Indicator, Stress-Strain Curve and Volume Change

Behaviour during Shearing for Size 0.6mm with Effective Stress 50kPa

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Breakageindicator


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0

50

100

150

200

250

300

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)


-2

0

2

4

6

8

10

12

14

0 5 10 15 20

Axial strain (%)

Volumechange(ml)

Figure 4.2 (b): The Breakage Indicator, Stress-Strain Curve and Volume Change


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Breakageindicator


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0

100

200

300

400

500

600

700

800

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)


-2

0

2

4

6

8

10

12

14

0 5 10 15 20

Axial strain (%)

Volumechange(ml)

Figure 4.2 (c): The Breakage Indicator, Stress-Strain Curve and Volume Change


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Breakageindicator


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0

100

200

300

400

500

600

700

800

900

0 5 10 15 20

Axial strain (%)

D

eviatorstress(kPa)


-2

0

2

4

6

8

10

12

14

0 5 10 15 20

Axial strain (%)

Volumechang

e(ml)

Figure 4.2 (d): The Breakage Indicator, Stress-Strain Curve and Volume Change


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0

200

400

600

800

1000

1200

0 2 4 6 8 10 12 14 16 18

Axial strain (%)

Deviatorstress(kPa)


-10

-5

0

5

10

15

0 2 4 6 8 10 12 14 16 18

Axial strain (%)

Volumechange(ml)

Figure 4.2 (e): The Breakage Indicator, Stress-Strain Curve and Volume Change


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Breakageindicator


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0

50

100

150

200

250

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)


-2

0

2

4

6

8

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12

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16

18

20

0 5 10 15 20

Axial strain (%)

Volume

change(ml)



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Breakageindicator


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0

50

100

150

200

250

0 2 4 6 8 10 12 14

Axial strain (%)

D

eviatorstress(kPa)


-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 2 4 6 8 10 12 14

Axial strain (%)

Volumechang

e(ml)



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Breakageindicator


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0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16

Axial strain (%)

Deviatorstress(kPa)


-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 2 4 6 8 10 12 14 16

Axial strain (%)

Volumech

ange(ml)



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Breakageindicator


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0

100

200

300

400

500

600

700

800

900

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)


-2

0

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4

6

8

10

12

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16

18

20

0 5 10 15 20

Axial strain (%)

Volumech

ange(ml)



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Breakageindicator


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0

200

400

600

800

1000

1200

1400

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)


-2.0

0.0

2.0

4.0

6.0

8.0

10.0

0 5 10 15 20

Axial strain (%)

Volumechang

e(ml)



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Breakage

indicator


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0

20

40

60

80

100

120

140

160

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)


-4

1

6

11

16

21

26

31

36

0 5 10 15 20

Axial strain (%)

Volume

change(ml)


Behaviour during Shearing for Size 2mm with Effective Stress 50kPa

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Breakageindicator


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0

50

100

150

200

250

300

350

0 5 10 15 20

Axial strain (%)

Deviatorstress(kPa)


-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 5 10 15 20

Axial strain (%)

Volumecha

nge(ml)



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Breakage

indicator


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0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16

Axial strain (%)

Deviatorstress(kPa)


-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 2 4 6 8 10 12 14 16

Axial strain (%)

Volumecha

nge(ml)



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0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12 14 16

Axial strain (%)

Deviatorstress(kPa)


-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 2 4 6 8 10 12 14 16

Axial strain (%)

Volumecha

nge(ml)



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Breakage

indicator


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0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14

Axial strain (%)

Deviatorstress(kPa)


-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 2 4 6 8 10 12 14

Axial strain (%)

Volum

echange(ml)



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Breakageindicator


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The stress-strain curve is calculated with membrane penetration correction. The

correction must be done because the actual deviator stress given by the data

logger is based on the initial specimen area, which is 50mm. However, the

deviator stress must be calculated based on the area of specimen before the

shearing stage, which is the area during consolidation stage. During

consolidation stage, the specimen experiences contraction which results

membrane penetration. Hence, correction must be done to the deviator stress.

The sample calculation of corrected deviator stress for size 0.6mm with

effective stress 400kPa is given below.

Deviator Stress Correction Due to Membrane Penetration

Mass of soil = 299.53 kg

Membrane thickness = 0.2 mm

Average diameter of specimen, D0 (ave) = (dtop + dmidheight + dbase) / 3

= (50.3 + 50.4 + 50.45)/3

= 50.4 mm

Initial diameter of specimen, Do = D0 (ave) (2 x Membrane thickness)

= 50.4 0.4

= 50.0 mm

Initial area of specimen, Ao = (/4)(D02)

= (/4)(50.02)

= 1963.5 mm2

= 1.9635 x 10-3 m2

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Initial length of specimen, Lo = 99.9mm

= 0.0999m

Initial volume of specimen, Vo = A0 xL0

= (1.9635 x 10-3)x (0.0999)

= 1.9615 x 10-4 m3

Membrane Penetration Correction

Length of specimen at the end

of consolidation, L end consolidation = L0 Vertical displacement, L

= 99.9 0.016

= 99.884 mm

= 0.09988 m

Initial volume, Vo = (Aend consolidation x L end consolidation) + Volume change

A end consolidation = (Initial volume,Vo - Volume change)/ L end consolidation

= [1.9664 x 10-4 (1.97 x 10-6)] / 0.09988

= 1.949 x 10-3 m2

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Area Correction, A

A x L end consolidation = h x A V

A x L end consolidation = (L end consolidation -h) x A V

A = (A x L end consolidation V)/(h- h)

where:-

A = Area correction

h = Height of specimen during shearing stage

h = Change in height

V = Volume change during shearing stage

A = [(1.949 x 10-3 )(0.09988) + (2.91x10-6)] / (0.09988-0.0084)

A = 2.16 x 10-3 m2

Force, P = A x

= (1.949 x 10-3 )(1212.6)

= 2.36 kN

Deviator stress corrected, c = Axial Load/ Corrected area

= P/A

= (2.36) / (2.1 x 10-3)

= 1127.02 kN/m2

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Hence, from the calculation, it can be seen that the corrected deviator stress

due to membrane penetration is 1127.02kN/m2, which is 85.58kN/m2 lower

than the actual deviator stress. It is approximately 10% reduction from the

actual deviator stress.

4.3 Strength Characteristics

The strength characteristics are gathered from Mohr circle plot. Figure 4.5(a)

shows the Mohr circle plot for sand with size 0.6mm, Figure 4.5(b) shows the

Mohr circle plot for sand with size 1.18mm and Figure 4.5(c) shows the Mohr

circle plot for sand with size 2mm.

For grain size 0.6mm, it can be seen that there are only specimen with effective

stress 300kPa and 400kPa touch the failure envelope. Other specimens are

lying under the failure envelope. The same situation happened for grain size

1.18mm, where only specimen with effective stress 50kPa, 200kPa and 300kPa

touch the failure envelope. For grain size 2mm, all specimens touch the failure

envelope except specimen with effective stress 400kPa. There is an abnormal

result gathered for this specimen, where the deviator stress that forms the Mohr

circle radius is too high. From the graph plotted, the internal friction angle for

size 0.6mm, 1.18mm and 2mm is 30o, 33o and 32o respectively.

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CHAPTER 5

DISCUSSION

5.1 The Significant of Particle Breakage Research

The significant of particle breakage research is that it affected the soil strength.Although it is considered as not so important because the effect is in a long

term and quite visible, but it is actually an important aspect when it comes to

strength factor. It is a matter of safety as if the strength decrease, it will cause

decrease in safety too. For instance, stability of tall earth dams rely on the

safety of the earth dams to support the hydrostatic pressure. In a long run, there

is possibility of failure if a precise analysis is not conducted on the dams.

Moreover, many of the existing analysis models do not consider the effect of

particle breakage; hence it is important to study this aspect so that the existing

analysis can be improved in the future.

The objective of this research is to study the effect of particle breakage to the

stress-strain curve. The study covers consolidated isotropically drained (CID)

triaxial tests on course grained soils at low (< 300 kPa) and high (> 300 kPa)

confining pressures. The scope of work for this study is to detect particle

breakage using Sony Sound Forge software and through particle size

distribution curve after triaxial test. Furthermore, this research is intended to

determine the shape of the shear strength envelope in effect of particle

breakage. After completing this research, all of the objectives have been

successfully fulfilled.

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5.2 Particle Breakage Indications

The particle size distribution is conducted to the specimen in order to identify

the particle breakage. It is a mean to quantify finer particles produced after

shearing stage in triaxial test. However, particle size distribution is not a best

solution to identify particle breakage especially in the test which involved very

fine soil. It is because the fine particles produced after shearing can be

diminished due to transportation from triaxial machine to the sample box, then

it will be transferred to the sieving pan. It involved very careful handling and it

is quite impossible to achieve. Hence, a better solution in identifying particle

breakage is by recording the sound produced during shearing stage. It is a way

to identify breakage and a more comprehensive way in order to identify which

part in the shearing stage recorded breakage.

The sound detection is conducted in order to know which part of the stress-

strain curve experience particle breakage. The sound is gathered via

microphone which mounted on the cell body. The microphone is connected to

laptop and the frequency produce in the cell body is recorded by Sony Sound

Forge software. The sound produce in the cell body not solely comprised of

particle breakage sound. There is also noise produce by the triaxial machine.

The noise is detectable since the breakage sound produced higher frequency

than the noise. However, the plain test in conducted in order to record the

machine sound alone. Figure 5.1 shows the sound produce with no specimen.

There is no specimen installed in the cell body. Therefore, it is easier to

distinguish between the particle breakage sound and the machine sound.Actually it is a challenge to publish sound on the paper. However, the Sony

Sound Forge software made possible to present the breakage sound via

frequency recorded.

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Figure 5.1: The Sound Produce without Specimen

From the entire specimen tested, all of them experienced particle breakage. The

amount of finer particle produced is quite small, but it is enough to prove that

breakage happened even for tests which involved low effective stress.

McDowell and Khan (2003) stated that there is limited evidence on particle

breakage during creep. It is difficult to identify breakage due to the fine particle

produced is really small. This research has proved that particle breakage occur

during creep by recording the sound produced when the soil experience

straining under constant stress at the end of the test. However, the sound wave

generated may also due to friction between the sand particles during shearing

process. Therefore, it is essential to conduct a test to determine the intensity of

wave generated due to friction alone.

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The test of determining the friction frequency is conducted by rubbing sand

particles using fingers. The sound of frictions between sand particles and sound

indication during shearing are given in Figure 5.2. It can be seen that the

frequency produced due to friction is quite small. By comparing friction sound

and the sound produced during shearing process, it can be seen that there are

sounds which exceeded the friction sound. It is suspected breakage sound has

higher frequency than friction sound. So, breakage is still proved to take place

during shearing process.

`

`Figure 5.2: The Sound of Frictions between Sand Particles and Sound

Indication during Shearing

57

Sound indication (i.e size 0.6mm;

effective stress 200kPa)

Friction indicator 3

Friction indicator 1 Friction indicator 2


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5.3 Particle Breakage during Dilation

Dilation is a process where soil particles roll to each other and cause the

specimen to expand. Particle breakage can be identified at this stage. The

process of dilation can be detected just before the peak strength through the

sound recorded. The dilation process influenced the magnitude of the peak

strength; hence it is an important process to be focused in order to predict the

peak strength.

Dilation process is a boundary to be reached by the soil particles before it

achieved the peak strength. The soil particles have it own grain strength,

whether it is hard or weak. It will break easily if it is a weak particle and has

angular shape. The condition of soil particles arrangement also influences the

particle breakage. The dense sand dilates while the loose sand shrink, hence the

peak strength characteristics between these two soils states are slightly

different. The peak strength can be higher if the sand consists of a hard,

rounded shape and in dense state.

5.4 Particle Breakage and Stress-Strain Behaviour

The stress-strain behaviour of the specimens tested is according to the typical

shape of stress-strain curve. The stress-strain curve is steeped before the peak

strength and it form a concave after peak strength. The shape of the stress-

strain curve is influence by the relative density of the specimen. The denser

state specimens will exhibit dilation while loose state specimens only showconstant straining immediately after the peak strength.

The particle breakage indications can be detected through the sound recorded.

There is also an obvious indication of particle breakage in the stress-strain

curve as the respective axial strain at failure for the specimen with the same

size but with different confining pressure is not coincide on the same axial

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strain. The particle breakage activity has shifted the peak strength to the right

as confining pressure increase. The explanation for this phenomenon is that

while breakage commence, the soil particles are breakdown to finer state. It

results different shear plane for the specimen, although the specimens

constitute of the same size. The specimen with higher confining pressure

recorded higher degree of particle breakage while those with lower confining

pressure show lower amount of particle breakage. The shear plane with finer

particles will result lower friction angle. This is why in Mohr circle, the shear

strength envelope at failure tends to curve at higher confining pressure. Hence,

from this situation it can be concluded that the shifted axial strain is due to the

different patent of particles structure on the shear plane.

Figure 5.3 (a) shows the deviator stress versus axial strain for size 0.6mm.

From the stress-strain curve, it can be seen that there are some specimens

exhibit loose sand and some are in dense state. The variation is given by the

way of compaction while in preparation stage. The specimen is prepared to

exhibit dense state. However, there are some specimens do not achieved dense

state such as specimens with 50kPa and 100kPa. Other specimens with higher

confining pressure illustrate dense sand. There is obvious peak strength in the

stress-strain curve for these specimens. The specimens dilate before reach the

peak strength.

Figure 5.3 (b) shows the volume change behavior for size 0.6mm. From thisgraph, it can be seen that there are dilation process occur on specimen with

effective stress 200kPa, 300kPa and 400kPa. The dilation process is denoted by

the increase in volume change on the early stage and formed peak strength at

certain axial strain. The dilation process involved expansion of specimen,

which is why the volume increases.

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Deviator stress vs axial strain for size 0.6

0

200

400

600

800

1000

1200

Axial strain (%)

Deviatorstress(kPa)

Eff.stress = 50kPa

Eff.stress = 100kP

Eff.stress = 200kP

Eff.stress = 300kP

Eff.stress = 400kP

Figure 5.3(a): The Deviator Stress versus Axial Strain for Size 0.6mm

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Volume change vs axial strain during shearing for size

0.6mm

-2

0

2

4

6

8

10

12

14

16

0 5 10 15 20 2

Vol.change(ml)

Eff.stress=50kPa

Eff.stress=100kPa

Eff.stress=200kPa

Eff.stress=300kPa

Eff.stress=400kPa

Figure 5.3(b): The Volume Change Behavior for Size 0.6mm

Figure 5.4 (a) shows the stress-strain curve for size 1.18mm. From the graph

plotted, it can be seen that specimen with low confining pressures (50kPa and

100kPa) exhibit loose state sand while specimen with high confining pressures

show dense state sand. It is observed that the specimen with low confining

pressures also dilate but it is not so obvious. The rate of dilation for specimen

with high confining pressures is more obvious because when shearing stage

commence, these specimens are imposed with high confining pressure, hence

the sand particles have higher resistance to dilate. Therefore the peak strengthwill be higher and the stress will decrease steeply after the peak strength.

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Deviator stress vs axial strain for size 1.18mm

0

200

400

600

800

1000

1200

1400

Axial strain (%)

Deviatorstress(kPa)

Eff.stress = 50kPa

Eff.stress = 100kPa

Eff.stress = 200kPa

Eff.stress = 300kPa

Eff.stress = 400kPa

Figure 5.3 (a): The Stress-Strain Curve for Size 1.18mm

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Volume change vs axial strain during shearing for size

1.18mm

-5

0

5

10

15

20

0 5 10 15 20 2

Vol.change(ml)

Eff.stress=50kPa

Eff.stress=100kPa

Eff.stress=200kPa

Eff.stress=300kPa

Eff.stress=400kPa

Figure 5.4(b): The Volume Change Behavior for Size 1.18mm

Figure 5.4 (b) shows the volume change behaviour for size 1.18mm. The

specimens with high confining pressure dilated, while the specimens with low

confining pressure shrink. The curve for specimen 100kPa is actually move

towards volume change curve of 200kPa and it is intersecting the curve. That is

why the curve is plotted until axial strain 6% only. It is observed to be an error

that can be due to the volume change unit apparatus. The volume change unit

gathered the volume of water that flowing in and out of the specimen. The

curve for specimen 100kPa is flattening due to the failure of the volume changeunit to record the volume of water going out of the specimen. Actually the

curve must be situated between 200kPa and 50kPa.

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Deviator stress vs axial strain for size 0.6mm

0

200

400

600

800

1000

1200

1400

1600

Axial strain (%)

Deviatorstress(kPa)

Eff.stress = 50kPa

Eff.stress = 100kPa

Eff.stress = 200kPa

Eff.stress = 300kPa

Eff.stress = 400kPa

Figure 5.5(a): The Stress-Strain Curve for Size 2mm

Figure 5.5(a) shows the stress-strain curve for size 2mm while Figure 5.5(b)

illustrates the volume change behaviour for size 2mm. From the result

obtained, almost all of the specimens exhibit dense state sand. Specimen with

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confining pressure 50kPa shows low rate of dilation while specimens with high

confining pressures have more obvious peak strength resulted from the dilation

process. Moreover, the peak strength for different effective stress is not

coinciding on the same axial strain. This is due to the effect of particle

breakage. The other grain size sand also experiences this and it is proved that

particle breakage has direct effect on the stress-strain curve. Figure 5.4(b)

shows the volume change behaviour for size 2mm. The specimen with

confining pressure 200kPa, 300kPa and 400kPa show that there is dilation

process happened during shearing. The higher confining pressure results flatter

curve.

Volume change vs axial strain during shearing

-5

0

5

10

15

20

25

0 5 10 15 20 25

Vol.change(ml)

Eff.stress=50kPa

Eff.stress=100kPa

Eff.stress=200kPa

Eff.stress=300kPa

Eff.stress=400kPa

Figure 5.5(b): The Volume Change Behaviour for Size 2mm

5.5 Particle Breakage Effects on the Shear Strength Failure Envelope

The strength characteristic is given by the friction angle in the Mohr circle. The

internal friction is the resistance to shear stresses which generated by the

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interlocking of the soil particles. From the graph plotted, the friction angle for

size 0.6mm, 1.18mm and 2mm is 30o, 33o and 32o respectively.

The shear strength failure envelope is identified to be curved at low effective

stress and form a straight line at higher confining pressure. The curvature of the

shear strength failure envelope is influenced by the relative density of the

specimen. The denser sand results more curvature than the loose sand.

However, there are some Mohr circle do not touch the failure envelope line.

For instance, for size 0.6mm, the Mohr circle for effective stress 50kPa,

100kPa and 300kPa are not touching the failure line due There is also

possibility of the highest effective stress, which is 400kPa results higher

deviator stress. Hence, the Mohr circle is bigger and it gives effect on the

failure envelope. So, the friction angle will be higher due to this situation.

5.6 The Effect of Particle Breakage to Strength

The effect of particle breakage to the strength of soil is still less understood. In

theory, particle breakage resulted higher deviator stress in the stress strain

curve when particle breakage commence. The stress-strain curve will

continuously increase with the increase of axial strain. However, this

phenomenon can only happen in a very dense specimen. It is because when the

specimen is in very dense state, the soil particles will have little room to move.

Dilation is diminished at this point, where the strain-strain curve of very dense

sand tends to exhibit like in loose state. The increase in deviator stress willonly stopped at certain axial strain which is abnormally higher than usual.

The continuous increase in deviator stress cannot be seen in this study. It is

hard to replicate very dense sand state. It involved modification on the

membrane rubber used and also the ability of the pressure pump to supply

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enough pressure. Moreover, the packing of soil when in preparation stage can

cause initial particle breakage before the test commence. For this study,

breakage is prohibited during preparation stage because the objective of the

study is to prove that breakage occur during shearing stage. Particle breakage is

proved in the particle size distribution besides sound recording. Hence, initial

breakage can influence the resulted particle size distribution graph.

5.7 Future Development In Soil Mechanics Model By Considering Particle

Breakage Effects

Many of the existing soil mechanics model do not consider the effect of

particle breakage. The effect of particle breakage is significant as it maybe

results lower peak strength. Therefore, the predicted peak strength by existing

model might be higher than the actual results. Hence, it is quite unsafe to use

this predicted result.

The dilatancy and compressibility concept that related to Mohr-Coulomb

friction angle is introduced in soil mechanics by Taylor (1948), Bishop (1954)

and Rowe (1962). This concept which based on energy theory of stress

dilatancy studied the additional strength that can be deduced due to volumetric

dilation. However, the concept does not consider particle breakage. Bolton

(1986) developed dilatancy index, which suggested that there is relationship

between strength and rate of volume change. It is also not considering particle

breakage effect. But one thing can be highlighted here is it is actually not thevolume change govern the strength, but it is the mobilized shear strength that

influence the strength.

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CHAPTER 6

CONCLUSION AND RECOMMENDATIONS

The particle breakage is a factor that must be considered in design. It is because

particle breakage has direct effect to the stress-strain curve. Particle breakage occurs

not only in soil with high confining pressure. This study proved that particlebreakage happened even in low confining pressure (i.e. 50kPa).

The particle breakage can be easily detected in stress-strain curve through the peak

strengths that do not coincide on the same axial strain. The shifted axial strain is due

to the different patent of particles structure on the shear plane, which is due to

particle breakage. Higher confining pressure results more breakage, hence the peak

strength tend to shift to the right with increasing confining pressure. Therefore,

particle breakage is the dominant factor that cause failures occur at different axial

strain in the stress-strain curve.

Particle breakage results curvature on the failure envelope in Mohr circle. The failure

envelope is well known to be curved at low pressure, but due to particle breakage,

the failure envelope tends to be curved at high pressure too. The curvature is due to

reorientation of particle when breakage commence.

Particle breakage also influences the strength of soil. In theory, particle breakage

causes the deviator stress to continuously increase. Hence, the strength will increase

if particle breakage commence.

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The results obtained from the test have proved that particle breakage had occurred

during dilation. This is due to slippage of soil particles to accommodate the applied

load. The dilation process is detected via sound recording during shearing stage.

Particle breakage is more prone to the angular shape sand particles. This research

used quartz sand with angular shape, hence the dilation process has resulted more

breakage.

This study can be improved if the breakage indicator can measure the frequency

produce in real time. Hence, the data can be clearly interpreted for certain important

part on the stress-strain curve that experience particle breakage.

The continuous increase in the stress-strain curve cannot be shown in this study

because the specimen is not dense enough. Hence, it is recommended that the

specimen must be compacted very well and double membrane rubber must be used in

order to avoid leakage.

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